<!DOCTYPE html>

<html>

<head lang="en">
  <meta charset="UTF-8">
  <title></title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    table {
      border-collapse: collapse;
      border-spacing: 0;
      border: 1px solid #c0c0c0;
      width: 500px;
      margin: 100px auto;
      text-align: center;
    }

    th {
      background-color: #09c;
      font: bold 16px "微软雅黑";
      color: #fff;
      height: 24px;
    }

    td {
      border: 1px solid #d0d0d0;
      color: #404060;
      padding: 10px;
    }

    .allCheck {
      width: 80px;
    }
  </style>
</head>

<body>
  <table>
    <tr>
      <th class="allCheck">
        <input type="checkbox" name="" id="checkAll"> <span class="all">全选</span>
      </th>
      <th>商品</th>
      <th>商家</th>
      <th>价格</th>
    </tr>

    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米手机</td>
      <td>小米</td>
      <td>￥1999</td>
    </tr>

    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米净水器</td>
      <td>小米</td>
      <td>￥4999</td>
    </tr>

    <tr>
      <td>
        <input type="checkbox" name="check" class="ck">
      </td>
      <td>小米电视</td>
      <td>小米</td>
      <td>￥5999</td>
    </tr>
  </table>


  <script>
    const allCheck = document.querySelector('#checkAll')
    const cks = document.querySelectorAll('.ck')
    // console.log(allCheck);
    // console.log(cks);
    // 1.点击全选 -> 三个被勾选
    allCheck.addEventListener('click',function(){
      for(let i = 0 ; i < cks.length ; i++){
        cks[i].checked = allCheck.checked
    }
    })

    // 2.三个被勾选->全选被勾选
    for(let i = 0 ; i < cks.length ; i++){
    // 为每一个小复选框添加点击事件
      cks[i].addEventListener('click',function(){
        allCheck.checked = document.querySelectorAll('.ck:checked').length === cks.length
      })
    }
  </script>


</body>

</html>